1. Field of the Invention
This invention relates to a method of controlling a solenoid actuator and, more particularly, to a method of controlling a solenoid actuator in such a way as to eliminate variations in the attracting force due to hysteresis characteristics.
2. Description of the Related Art
FIG. 3 shows the current/attracting force characteristics of a solenoid actuator. A hysteresis loop is drawn in which the characteristic produced when the drive current I is increased from zero and the characteristic produced when the current is reduced from its maximum value are not coincident. As shown in FIG. 4, in case (a), the drive current I is increased to a target current value IT. In case (b), the current is reduced from a current value higher than the target current value IT and reaches the target current value IT. As shown in FIG. 5, the case (b) exhibits stronger attracting force f than the case (a).
Depending on the mode of use of the solenoid actuator, variations in the attracting force due to hysteresis characteristics may present no problems. However, where more accurate control of attracting force is necessary, hysteresis characteristics pose problems.
For example, in a cutting machine for a cut sheet for making cut lettering by driving a cutting head up and down by a solenoid actuator or in a pen plotter for drawing figures by vertically driving a pen head by a solenoid actuator, where soft landing control for increasing the drive current from zero to a target value and speed landing control for reducing the current to the target value immediately before the cutter or pen is made to land by passing a large current through the solenoid to lower the head at a high speed are performed, the pressure of ground contact of the cutter or pen varies depending on the control method.
Accordingly, a technical problem to be solved occurs to eliminate variations in the attracting force due to the hysteresis characteristics of a solenoid actuator. The present invention is intended to solve the foregoing problem.
This invention is proposed to achieve the above-described object, and provides a method of controlling a solenoid actuator, the method including the step of: canceling hysteresis characteristics of the solenoid actuator by solenoid drive current control means that stabilizes a solenoid drive current to a target value through a swinging period in which the solenoid drive current is swung up and down about the target value when the solenoid drive current is controlled toward the target value.